Alaska's Little Sitkin Volcano Stirs

AVO is reporting that seismic activity has picked up at Little Sitkin volcano in the Aleutian Arc. Little Sitkin is one of the farthest volcanoes from mainland Alaska, and is about halfway from Alaska to Russia's Kamchatka peninsula. The volcano does not have a record of historical eruptions, however evidence on the island suggest it may have erupted early last century. A series of sharp and frequent quakes has rattled the island, and has prompted AVO to raise the aviation code from unassigned to "Yellow" (advisory).

AVO's statement is below:

"At approximately 19:15 AKDT (04:15 UTC) last night, a swarm of high-frequency earthquakes began at Little Sitkin Volcano. The continuation of this anomalous seismic activity through the night prompts AVO to raise the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. No eruptive activity is currently indicated.

AVO is closely monitoring the situation and will issue further updates as conditions changes.Little Sitkin is monitored by a 4-station seismic network as well as satellite imagery. Little Sitkin Island is located 35 km (21 mi) northwest of Amchitka and 320 km (200 mi) west of Adak in the remote western Aleutian Islands. The last eruption of Little Sitkin is questionable and may have been in the early 1900s."

The Smithsonian GVP characterizes the volcano here:

"Diamond-shaped Little Sitkin Island is bounded by steep cliffs on the east, north, and NE sides. Little Sitkin volcano contains two nested calderas. The older, nearly circular Pleistocene caldera is 4.8 km wide, may have once contained a caldera lake, and was partially filled by a younger cone formed mostly of andesitic and dacitic lava flows. The elliptical younger caldera is 2.7 x 4 km wide; it lies within the eastern part of the older caldera and shares its eastern and southern rim. The younger caldera partially destroyed the lava cone within the first caldera and is of possible early Holocene age. Young-looking dacitic lava flows, erupted in 1828 (Kay, in Wood and Kienle 1990), issued from the central cone within the younger caldera and from a vent on the west flank outside the older caldera. Fumarolic areas are found near the western coast, along the NW margin of the older caldera, and from the summit crater down the southern flank for a 1 km distance."

With activity at this volcano now being closely watched, this brings the number of Alaskan volcanoes currently being monitored to three. Cleveland volcano has been having small to minor eruptions for about a year now, and Mt Iliamna was raised to Yellow alert following a series of very shallow quakes, and increased fumerolic activity, however no eruption has happened at Iliamna following what AVO suspects was a minor magma dike intrusion. This brings the total volcanoes in Alaska showing activity to three at this time. 

Large And Shallow Earthquake Swarm Near Aniakchak Volcano

Aniakchak volcano in Alaska is one of the largest, and most active volcanoes in the Aleutian arc. The volcano contains a 10km wide caldera, with multiple cinder cones occupying the ~3400 year old caldera floor. The last eruption of Aniakchak occurred in 1931, which marked the only known historical eruption of the volcano.

A large earthquake swarm struck approximately 25 miles NE of Aniakchak on August 3-5, centered between Aniakchak volcano and the lesser-known Yantari volcano (which apparently had a very Mt. St. Helens like eruption in pre-history). The largest quake was a 4.7 magnitude quake at a depth of around half a kilometer (which is very shallow). Many other shallow quakes, some with similar magnitudes have occurred (see the below image) since.

Google Earth plugin with USGS real-time overlay enabled showing the location of the quake swarm

The depths of most quakes in the area are usually some hundreds of KM deep, as this is a subduction zone where one plate slides underneath the other. Occasionally this process generates a magma vein, that results in dike intrusions and the birth of most of the world's stratovolcanoes.

This quake swarm is curious due to its location and the very shallow depths. New volcanoes have been born in Alaska in the past, sometimes with disastrous results such as the eruption of Novarupta, the largest eruption of a US volcano in recorded history. While it is likely that this is a magma dike intrustion into the crust, it is impossible to say what might occur if the swarm does not return, or no new magma is injected into the crust. Most dike intrusions do not result in an immediate eruption, and some times they never do.

In any case, I will be keeping a close eye on this, and possibly email AVO about the swarm and see if they were aware of it (which I am sure they were) and whether they might be able to shed some light on it for our readers. Stay tuned!

*****UPDATE 8/9/2012*****

Another single quake at a depth of 5km measuring 2.5 occurred today in the area. This is the first aftershock/tremor in a few days. I have contacted AVO requesting information on the current swarm, and hopefully will hear back from them soon!

*****UPDATE 8/10/2012*****

AVO responded to my email with the following response:

"They're regional tectonic earthquakes. We have no indication that these earthquakes have anything to do with volcanism.This series of earthquakes, at this time, is not alarming to us."

So it appears that there may be several faults criss-crossing the Aleutians that occasionally have these shallow types of quakes occur, even very near active volcanoes.